Aromatic polyimides, in particular aromatic polyetherimides, form a class of thermoplastic polymers that offer some excellent engineering properties such as very high heat resistance, excellent melt processability, good elongation properties and high impact resistance. They have also rather high strength, rather high stiffness and rather high fire resistance. Notwithstanding, in certain demanding industries such as commercial aviation and other civil transports, the level of properties achieved by aromatic polyimides, in particular polyetherimides, is insufficient.
Polyarylenes, especially polyphenylenes, exhibit an exceptionally high strength, stiffness and fire resistance; they exhibit also an exceptionally high hardness, scratch resistance and dimensional stability. As concerns these properties, the level of properties achieved by polyarylenes usually well exceeds that required by the most severe end uses. Unfortunately, polyarylenes have serious limitations in toughness-related properties, in particular in terms of impact resistance and elongation properties.
To meet the need for increased strength, stiffness and fire resistance, it has already been tried to blend certain aromatic polyimides, such as polyetherimides, with certain classes of polyarylenes, known as Parmax® 1000 and 1200 polyphenylenes (Parmax® 1200 is now commercialized by SOLVAY ADVANCED POLYMERS under the trade name PRIMOSPIRE™ PR-120). While in these aromatic polyimide-polyarylene blends of the prior art, the polyarylene provides indeed an exceptionally high level of strength and stiffness (which usually exceeds the level needed in the most severe aircraft and other civil transportation applications), these blends have still some limitations in terms of fire resistance. Besides, as the skilled in the art may have have dreaded in the light of the properties of neat polyarylenes, the prior art aromatic polyimide-polyarylene blends suffer from limitations in terms of elongation properties and impact resistance; also, they have rather poor, or even poor, melt compatibility and processability, which probably explains why the skilled person generally prepared them either by solution blending or by reactive blending (e.g. starting from macromers of rigid-rod polyphenylenes).
Polymer blends have been widely taught and employed in the art. As broad as this statement may be, the blending of polymers remains an empirical art and the selection of polymers for a blend giving special properties is, in the main, an Edisonian-like choice. Certain attributes of polymer blends are more unique than others. The more unique attributes when found in a blend tend to be unanticipated properties. According to Zoller and Hoehn, Journal of Polymer Science, Polymer Physics Edition, vol. 20, pp. 1385-1397 (1982): “Blending of polymers is a useful technique to obtain properties in thermoplastic materials not readily achieved in a single polymer. Virtually all technologically important properties can be improved in this way, some of the more important ones being flow properties, mechanical properties (especially impact strength), thermal stability, and price. ( . . . ) Ultimately, the goal of such modeling and correlation studies should be the prediction of blend properties from the properties of the pure components alone. We are certainly very far from achieving this goal.”
In the field of miscibility or compatibility of polymer blends, the art has found predictability to be unattainable, even though considerable work on the matter has been done. According to authorities, “It is well known that, regarding the mixing of thermoplastic polymers, incompatibility is the rule and miscibility and even partial miscibility is the exception. Since most thermoplastic polymers are immiscible in other thermoplastic polymers, the discovery of a homogeneous mixture or partially miscible mixture of two or more thermoplastic polymers is, indeed, inherently unpredictable with any degree of certainty, for example, see P. J. Flory, Principles of polymer Chemistry, Cornell University Press, 1953, Chapter 13, page 555.”
There remains a strong need for a polymer material offering a superior balance of properties, including at least part of, and preferably all, the following ones:                very high strength, higher than that of prior art neat aromatic polyimides;        very high stiffness, higher than that of prior art neat aromatic polyimides;        high fire resistance, higher than that of prior art neat aromatic polyimides and aromatic polyimide-polyarylene blends;        good elongation properties, in progress with regard to those of the prior art aromatic polyimide-polyarylene blends;        high impact resistance, higher than that of the prior art aromatic polyimide-polyarylene blends, and ideally approaching or even exceeding by certain aspects that of the neat aromatic polyimides; and        good melt processability, in substantial progress when compared to that of the prior art aromatic polyimide-polyarylene blends.        